Fluorescence-Based Selection of Gene-Corrected Hematopoietic Stem and Progenitor Cells From Acid Sphingomyelinase-Deficient Mice: Implications for Niemann-Pick Disease Gene Therapy and the Development of Improved Stem Cell Gene Transfer Procedures

Cationic Amphiphilic Drugs Boost the Lysosomal Escape of Small Nucleic Acid Therapeutics in a Nanocarrier-Dependent Manner

Small nucleic acid (NA) therapeutics, such as small interfering RNA (siRNA), are generally formulated in nanoparticles (NPs) to overcome the multiple extra- and intracellular barriers upon in vivo administration. Interaction with target cells typically triggers endocytosis and sequesters the NPs in endosomes, thus hampering the pharmacological activity of the encapsulated siRNAs that occurs in the cytosol. Unfortunately, for most state-of-the-art NPs, endosomal escape is largely inefficient. As a result, the bulk of the endocytosed NA drug is rapidly trafficked toward the degradative lysosomes that are considered as a dead end for siRNA nanomedicines. In contrast to this paradigm, we recently reported that cationic amphiphilic drugs (CADs) could strongly promote functional siRNA delivery from the endolysosomal compartment via transient induction of lysosomal membrane permeabilization. However, many questions still remain regarding the broader applicability of such a CAD adjuvant effect on NA delivery. Here, we report a drug repurposing screen (National Institutes of Health Clinical Collection) that allowed identification of 56 CAD adjuvants. We furthermore demonstrate that the CAD adjuvant effect is dependent on the type of nanocarrier, with NPs that generate an appropriate pool of decomplexed siRNA in the endolysosomal compartment being most susceptible to CAD-promoted gene silencing. Finally, the CAD adjuvant effect was verified on human ovarian cancer cells and for antisense oligonucleotides. In conclusion, this study strongly expands our current knowledge on how CADs increase the cytosolic release of small NAs, providing relevant insights to more rationally combine CAD adjuvants with NA-loaded NPs for future therapeutic applications.

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives is described, and the utility of the probes demonstrated by co-localization studies with visible wavelength fluorescent sphingosine derivatives.

Sperm abnormalities in heterozygous acid sphingomyelinase knockout mice reveal a novel approach for the prevention of genetic diseases

Acid sphingomyelinase knockout mice are a model of the inherited human disorder types A and B Niemann-Pick disease. Herein, we show that heterozygous (ASMKO(+/-)) mice have two distinct sperm populations resembling those found in normal and mutant animals, respectively, and that these two populations could be distinguished by their morphology, ability to undergo capacitation or the acrosome reaction, and/or mitochondrial membrane potential (MMP). The abnormal morphology of the mutant sperm could be normalized by demembranation with detergents or by the addition of recombinant acid sphingomyelinase to the culture media, and the corrected sperm also had an enhanced fertilization capacity. Methods were then explored to enrich for normal sperm from the mixed ASMKO(+/-) population, and flow cytometric sorting based on MMP provided the best results. In vitro fertilization was performed using ASMKO(+/-) oocytes and sperm before and after MMP sorting, and it was found that the sorted sperm produced significantly more wild-type pups than nonsorted sperm. Sperm sorting is much less invasive and more cost-effective than egg isolation, and offers several advantages over the existing assisted reproduction options for Niemann-Pick disease carrier couples. It therefore could have a major impact on the prevention of this and perhaps other genetic diseases.

Effects of Acid Sphingomyelinase Deficiency on Male Germ Cell Development and Programmed Cell Death1

Deficiency of acid sphingomyelinase (ASM), an enzyme responsible for producing a pro-apoptotic second messenger ceramide, has previously been shown to promote the survival of fetal mouse oocytes in vivo and to protect oocytes from chemotherapy-induced apoptosis in vitro. Here we investigated the effects of ASM deficiency on testicular germ cell development and on the ability of germ cells to undergo apoptosis. At the age of 20 weeks, ASM knock-out (ASMKO) sperm concentrations were comparable with wild-type (WT) sperm concentrations, whereas sperm motility was seriously affected. ASMKO testes contained significantly elevated levels of sphingomyelin at the age of 8 weeks as detected by high-performance, thin-layer chromatography. Electron microscopy revealed that the testes started to accumulate pathological vesicles in Sertoli cells and in the interstitium at the age of 21 days. Irradiation of WT and ASMKO mice did not elevate intratesticular ceramide levels at 16 h after irradiation. In situ end labeling of apoptotic cells also showed a similar degree of cell death in both groups. After a 21-day recovery period, the numbers of primary spermatocytes and spermatogonia at G2 as well as spermatids were essentially the same in the WT and ASMKO testes, as detected by flow cytometry. In serum-free cultures both ASMKO and WT germ cells showed a significant increase in the level of ceramide, as well as massive apoptosis. In conclusion, ASM is required for maintenance of normal sphingomyelin levels in the testis and for normal sperm motility, but not for testicular ceramide production or for the ability of the germ cells to undergo apoptosis.

Preimplantation diagnosis of a lysosomal storage disorder by in situ enzymatic activity: 'proof of principle' in acid sphingomyelinase-deficient mice

Genetic diagnosis of preimplantation embryos (PGD) can substantially reduce the chance that at-risk couples have children afflicted with inherited diseases. However, PGD requires DNA,which is usually obtained from single cells following embryo biopsy. In addition, PGD requires that the genetic defect(s) causing the disorder be known. We have therefore developed an alternative to PGD, which we term preimplantation enzymatic diagnosis (PED). PED has several advantages over PGD, including the facts that it does not require embryo biopsy and that the gene defect(s) causing the disorder need not be known. We have demonstrated 'proof of principle' for this approach using embryos obtained from a mouse model (ASMKO mice) of acid sphingomyelinase (ASM)-deficient Niemann-Pick disease, an inherited lysosomal storage disorder. For this technique, fluorescently (BODIPY)-conjugated sphingomyelin was used to detect ASM activity in situ. Wild-type, preimplantation embryos degraded the substrate following a short 'pulse-chase' period, resulting in markedly reduced fluorescence compared to ASMKO embryos, which retained the fluorescent substrate. Thus, the two embryo types could be easily distinguished by fluorescent microscopy. The fluorescent sphingomyelin was not toxic to the embryos, and the entire procedure could be accomplished within 48 h without embryo biopsy. We suggest that PED may be useful for the preimplantation diagnosis of lysosomal storage disorders, and perhaps other enzymatic defects where similar in situ assay methods are available.

Stem cell clonality and genotoxicity in hematopoietic cells: Gene activation side effects should be avoidable

Two serious adverse events involving activation of the LMO2 oncogene through retrovirus vector insertion in the otherwise extremely successful first gene therapy trial for X-linked severe combined immunodeficieny type 1 (SCID-X1) had initially caused widespread concern in the patient and research communities. Careful consideration 1 year after diagnosis of the second case still finds 12 of the treated patients clearly benefiting from gene therapy (freedom from treatment failure, 80%; survival 100%), a situation that should not portend the end of gene therapy for this disease, and is, in fact encouraging. While current approaches are justified to treat patients with otherwise life-threatening disorders, a broad consensus has developed that systematic basic research is required to further understand the pathophysiology of these serious adverse events and to provide new insights, enabling safer and more effective gene therapy strategies. With the continued success of SCID-X1 gene therapy in the majority of patients treated, it is of even greater importance to understand exactly which vector element or combination of elements predispose to toxicity. An in-depth study of the mechanisms behind the activation of the LMO2 and gammac genes will be highly instructive for the development of safer procedures and vectors. We summarize the central observations, ongoing experimental approaches, new concepts, and developments relevant to understanding, interpreting, and eventually overcoming the real and perceived obstacles posed by insertional mutagenesis due to gene transfer vectors.

Ex vivo gene therapy using bone marrow-derived cells: combined effects of intracerebral and intravenous transplantation in a mouse model of niemann–pick disease

Normal murine bone marrow cells were transduced with a retroviral vector to overexpress and release human acid sphingomyelinase (ASM). The transduced cells were then transplanted intravenously into 3-day-old, irradiated ASM-deficient mice, a model of human Niemann-Pick disease (NPD). At 4 weeks, engrafted mice received intracerebral injections of mesenchymal stem cells obtained from the original, transduced bone marrow. By 16 weeks, most of the treated NPD mice had near-normal levels of ASM activity in their tissues, including the brain; dramatically improved histology; and marked reductions in sphingomyelin. Cerebellar function also was normal, and the number of Purkinje cells was > 80% of normal. Remarkably, in certain regions of the cerebellum many of the surviving Purkinje cells expressed human ASM RNA, suggesting that either they were donor-derived or that the transplanted bone marrow cells had fused with existing Purkinje cells. However, despite these positive results, by 24 weeks the ASM activities were dramatically reduced and cerebellar function began to decline, coincident with the detection of anti-human ASM antibodies in the plasma. We conclude that this gene therapy procedure might be useful in Type A NPD and other neurological lysosomal storage disorders, particularly since it is an approach that could be beneficial for both the neurological and the visceral organ features of these diseases.

Correction of deficient CD34+ cells from peripheral blood after mobilization in a patient with congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is an inherited disease due to a deficiency in the uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme pathway. It is characterized by accumulation of uroporphyrin I in the bone marrow, peripheral blood, and other organs. The onset of most cases occurs in infancy and the main symptoms are cutaneous photosensitivity and hemolysis. For severe transfusion-dependent cases, when allogeneic cell transplantation cannot be performed, autografting of genetically modified primitive/stem cells is the only alternative. In the present study, efficient mobilization of peripheral blood primitive CD34(+) cells was performed on a young adult CEP patient. Retroviral transduction of this cell population with the therapeutic human UROS (hUS) gene resulted in both enzymatic and metabolic correction of CD34(+)-derived cells, as demonstrated by the increase in UROS activity and by a 53% drop in porphyrin accumulation. A 10-24% gene transfer efficiency was achieved in the most primitive cells, as demonstrated by the expression of enhanced green fluorescent protein (EGFP) in long-term culture-initiating cells (LTC-IC). Furthermore, gene expression remained stable during in vitro erythroid differentiation. Therefore, these results are promising for the future treatment of CEP patients by gene therapy.

Gene therapy for Fabry disease

Fabry disease is an X-linked metabolic disorder caused by a deficiency of alpha-galactosidase A (alpha-Gal A). Lack of this lysosomal hydrolase results in the accumulation of galactose-terminal glycosphingolipids in a number of tissues, including vascular endothelial cells. Premature death is predominantly associated with vascular conditions of the heart, kidneys and brain. Historically, treatment has largely been palliative. Alternative treatments for many lysosomal storage diseases have been developed, including allogeneic organ and bone marrow transplantation, enzyme replacement therapy, and gene therapy. Significant clinical risks still exist with allogeneic transplantations. Alpha-Gal A enzyme replacement therapy has been implemented in clinical trials. This approach has been effective but may have limitations for long-term systemic or cost-effective correction. As an alternative, gene therapy approaches, involving a variety of gene delivery systems, have been pursued for the amelioration of Fabry disease. Fabry disease is a compelling disorder for gene therapy, as target cells are readily accessible and relatively low levels of enzyme correction may suffice to reduce storage. Importantly, metabolic cooperativity effects are also manifested in Fabry disease, wherein corrected cells secrete alpha-Gal A that can correct bystander cells. In addition, a broad therapeutic window probably exists, and mouse models of Fabry disease have been generated to assist studies. As an example, in vitro and in vivo studies using alpha-Gal A-transduced haematopoietic cells from Fabry mice have demonstrated enzymatic correction of recipient cells and dissemination of alpha-Gal A upon transplantation, leading to reduced lipid storage in a number of clinically relevant organs. This corrective enzymatic effect has recently been shown to be even further enhanced upon pre-selection of therapeutically transduced cells prior to transplantation. This review will briefly detail current gene delivery methods and summarize results to date in the context of gene therapy for Fabry disease.

Niemann-Pick disease

Niemann-Pick disease, originally defined in terms of its histology as a reticuloendotheliosis, is now subdivided on the basis of biochemical and molecular criteria into two separate classes. This categorization has been aided by the discovery of the genes for acid sphingomyelinase, deficient in types A and B, and for the NPC-1 protein, deficient in types C and D, and the finding of mutations in each. Animal models of type A and type C disease are known or have been developed. These models have been utilized in therapeutic trials of bone marrow transplantation and gene transfection of stem cells and in studies of disease pathogenesis. Lysosphingomyelin has been implicated in the nervous system involvement associated with type A disease in humans and accumulations of the NPC-1 protein and apolipoprotein D have been found in murine NP-C brain. Cells from both human and murine Niemann-Pick disease type A have been studied to assess the role of acid sphingomyelinase in signal transduction pathways involving cell proliferation, differentiation, and apoptosis.

Hematopoietic stem cell gene therapy for Niemann-Pick disease and other lysosomal storage diseases

Of the various gene therapy approaches under investigation for the treatment of genetic diseases, hematopoietic stem cell-mediated gene therapy has attracted the most interest. Enriched populations of hematopoietic stem cells can be obtained from diseased individuals, genetically modified to express normal gene products, and then transplanted back into these individuals without the risk of graft versus host disease. Following transplantation and engraftment, hematopoietically-derived cells can repopulate various sites of pathology and express the normal gene product in vivo. Such a procedure has been accomplished in several mouse models of human genetics diseases, leading to partial or complete correction of the disease phenotype, and current efforts are now focused on adapting the success of murine systems to larger animals, including man. This review will focus on the use of hematopoietic stem cell-mediated gene therapy for the treatment of lysosomal storage disorders, and discuss recent data obtained in the laboratory using a murine knock-out mouse model of Types A and B Niemann-Pick disease (NPD).

Fluorescence-based selection of retrovirally transduced cells in congenital erythropoietic porphyria: direct selection based on the expression of the therapeutic gene

BACKGROUND

Congenital erythropoietic porphyria (CEP) is an inherited disease caused by a deficiency of uroporphyrinogen III synthase, the fourth enzyme of the haem biosynthesis pathway. It is characterized by accumulation of uroporphyrin I in the bone marrow, peripheral blood and other organs. The prognosis of CEP is poor with death occurring in early adult life and available treatments are only symptomatic and unsatisfactory. In vitro gene transfer experiments have documented the feasibility of gene therapy via haematopoietic stem cells to treat this disease. To facilitate future ex vivo gene therapy in humans, the design of efficient selection procedures to increase the frequency of genetically corrected cells prior to autologous transplantation is a critical step.

METHODS

An alternative selection procedure based upon expression of a transferred gene was performed on a lymphoblastoid (LB) cell line from a patient with congenital erythropoietic porphyria to obtain high frequencies of genetically modified cells. The presence of exogeneous delta-aminolevulinic acid (ALA), a haem precursor, induces an increase in porphyrin accumulation in LB deficient cells. Porphyrins exhibit a specific fluorescent emission and can be detected by cytofluorimetry under ultraviolet excitation.

RESULTS

In genetically modified cells, the restored metabolic flow from ALA to haem led to a lesser accumulation of porphyrins in the cells, which were easily separated from the deficient cells by flow cytometry cell sorting.

CONCLUSION

This selection process represents a rapid and efficient procedure and an excellent alternative to the use of potentially harmful gene markers in retroviral vectors.